utf16to8这个方法如何转gb2312

各位朋友，下面这个utf16to8的js方法，怎样将结果转为gb2312啊？
这是用js生成二维码的一个中文支持的方法。（http://www.cnblogs.com/pfbk/p/4848875.html就是这个），但现在只有国标的设备，只支持gb2312，所以要将utf8换成国标gb2312。

function utf16to8(str) {
var out, i, len, c;

out = "";
len = str.length;
for (i = 0; i < len; i++) {
    c = str.charCodeAt(i);
    if ((c >= 0x0001) && (c <= 0x007F)) {
        out += str.charAt(i);
    } else if (c > 0x07FF) {
        out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F));
        out += String.fromCharCode(0x80 | ((c >> 6) & 0x3F));
        out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));
    } else {
        out += String.fromCharCode(0xC0 | ((c >> 6) & 0x1F));
        out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));
    }
}

return out;

}

 //把编码转换成 gb2312编码
function UrlEncode(str)
{
 var i, c, ret="", strSpecial="!\"#$%&'()*+,/:;<=>?@[\]^`{|}~%";
 for(i = 0; i < str.length; i++)
 {
 //alert(str.charCodeAt(i));

 c = str.charAt(i);
 if(c==" ")
 ret+="+";
 else if(strSpecial.indexOf(c)!=-1)
 ret += "%" + str.charCodeAt(i).toString(16);
 if(z[str.charCodeAt(i)]　!= null)
 {
 d = z[str.charCodeAt(i)];
 try
 {
 ret += "%" + d.slice(0,2) + "%" + d.slice(-2);
 }
 catch (e)
 {
 alert(" $$ error name = " + e.name + ", message = " +e.message + ", d " + i + "= " + str.charCodeAt(i))
 }
 } //（jquery中文网 www.jquerycn.cn）
 else
 ret += c;
 }
 return ret;
 }
 function getSpell(str, sp)
 {
 var i, c, t, ret="";
 if(sp == null)
 sp="";
 for(i = 0; i < str.length; i++)
 {
 if(str.charCodeAt(i) >= 0x4e00)
 {
 c = parseInt(z[str.charCodeAt(i)], 16);
 if(c < 55290)
 {
 for(t = qswhSpell.length-1; t > 0; t = t - 2)
 if(qswhSpell[t] <= c)
 break;
 if(t > 0)
 ret += qswhSpell[t - 1] + sp;
 }
 }
 } a
 return ret.substr(0, ret.length-sp.length);
}

/// <summary>
        /// GB2312转换成UTF8
        /// </summary>
        /// <param name="text"></param>
        /// <returns></returns>
        public static string gb2312_utf8(string text)
        {
            //声明字符集   
            System.Text.Encoding utf8, gb2312;
            //gb2312   
            gb2312 = System.Text.Encoding.GetEncoding("gb2312");
            //utf8   
            utf8 = System.Text.Encoding.GetEncoding("utf-8");
            byte[] gb;
            gb = gb2312.GetBytes(text);
            gb = System.Text.Encoding.Convert(gb2312, utf8, gb);
            //返回转换后的字符   
            return utf8.GetString(gb);
        }

        /// <summary>
        /// UTF8转换成GB2312
        /// </summary>
        /// <param name="text"></param>
        /// <returns></returns>
        public static string utf8_gb2312(string text)
        {
            //声明字符集   
            System.Text.Encoding utf8, gb2312;
            //utf8   
            utf8 = System.Text.Encoding.GetEncoding("utf-8");
            //gb2312   
            gb2312 = System.Text.Encoding.GetEncoding("gb2312");
            byte[] utf;
            utf = utf8.GetBytes(text);
            utf = System.Text.Encoding.Convert(utf8, gb2312, utf);
            //返回转换后的字符   
            return gb2312.GetString(utf);
        } 

请各位朋友先仔细看看我的那段方法好吗？我就是要把最后return的out转成gb2312的。。